Hi Blueskies. Good luck with everything. I don't have any practical advice but as I'm on the other side of this situation, I thought I'd share.
I have been dating a chap for about 6 months. He had been a widower for about 6 months when we started seeing one another. We both have "grown-up children". But young grown-ups. His youngest is 21. The same age as my daughter.
I hope his kids are OK with it. It sounds like they are. A lot of teasing from his sons. "Oh you're not coming home tonight, Dad? Wonder why that is?"
I know he fibbed to his sons about how he met me. Told them he'd run into an old friend rather than tell them he was actively looking to meet someone on the Internet. Tbh, this was meant to be a FWB thing but feelings happened on both sides.
No plans to ever marry, move in together etc. I don't want to be his kids' "new mummy".
He talks about his late wife fairly frequently. Usually in a "sharing funny anecdotes from our past". She sounds great from what I've heard of her - funny, filthy and fiercely feminist. Apparently when she was dying, she told him he ought to get a girlfriend and/or a dog. He still wears his wedding ring. Which I think is completely normal.
When we got to the anniversary of his wife's death, I told him that I'll be as supportive as he wants me to be and understand if he wanted me to step away for however long.
I have (very briefly) met one of his sons and he has (very briefly) met my daughter.
I don't understand what he's going through. I have no experience of cancer or bereavement. I was a single parent from the off.
He's a lovely chap. We make each other laugh and look after one another. I would hate for him to be judged for dating me 6 months after his wife's death.
You sound like a nice chap too, OP.
Good luck with everything!